The nature of tissue processing requires that the samples be “fixed” prior to embedding in paraffin and micro-sectioning on a microtome to produce tissue sections suitable for immunostaining. The vast majority of fixation procedures, however, involve the use of aldehyde-based cross-linking agents, like formaldehyde and glutaraldehyde. During this process, molecular recognition elements of interest, epitopes and/or antigens are preserved using a formaldehyde treatment that produces chemical cross-linking which preserves the cellular features of the tissue. Formaldehyde preserves or fixes tissue or cells predominantly by cross-linking primary amine groups in proteins with other nearby nitrogen atoms in protein or nucleic acids through a —CH2— linkage. The process of tissue fixation however, frequently masks molecular recognition elements, antigens and/or epitopes for which detection is desirable for diagnostic, therapeutic, or prognostic purposes. The result is that the molecular recognition element, antigen and/or epitope of interest may be chemically modified or destroyed by reaction with aldehyde-based fixatives, making detection harder in fixed tissue. Thus, there is a recognized need in the art for improved methods for unmasking and retrieving molecular recognition elements, epitopes, molecules, and antigens of interest. Particularly, the prior art is deficient in methods and compounds that are easily formulated to reverse the aldehyde reaction in fixed tissue. The present invention fulfills this longstanding need and desire in the art.